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    <script>
        // 1. 想要一个变量自己加1   num = num + 1 比较麻烦
        let num = 1;
        num = num + 1; // ++num
        num = num + 1;
        console.log(num); // 3
        // 2. 前置递增运算符  ++ 写在变量的前面
        let age = 10;
        ++age; // 类似于 age = age + 1
        console.log(age);
        // 3. 先加1  后返回值
        let p = 10;
        console.log(++p + 10);
    </script>
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